Hundreds of thousands of people experience tendon ruptures and tendon detachments from bone annually. Rotator cuff tears are among the most common injuries observed by practitioners of sports medicine. Approximately 400,000 rotator cuff repair surgeries are performed in the United States annually.
The rotator cuff is a group of four tendons which converge and surround the front, back, and top of the head of the humerus shoulder joint. These tendons are connected individually to short muscles that originate from the scapula. The muscles are referred to as the “SITS” muscles-supraspinatus, infraspinatus, teres minor and subscapularis. The muscles function to provide rotation and elevate the arm and give stability to the shoulder joint. When the muscles contract, they pull on the rotator cuff tendons, causing the shoulder to rotate upward, inward, or outward. There is a bursal sac between the rotator cuff and acromion that allows the muscles to glide freely when moving.
Rotator cuff tendons are susceptible to tears, which are a common source of shoulder pain. The tendons generally tear off at their insertion (attachment) onto the humeral head. Injuries to the rotator cuff may be present as complete evulsions, or L- or U-type partial tears. Pain, loss of motion and weakness may occur when one of the rotator cuff tendons tears. When rotator cuff tendons are injured or damaged, the bursa often becomes inflamed and may be an additional source of pain.
Notwithstanding surgical instrumentation and advanced techniques, the incidence of re-injury following repair of the rotator cuff is high, with some estimates approaching 70%. The failure of rotator cuff repairs has been attributed to the poor healing and reattachment of the muscles that insert on the humeral head. The normal fibrotic and proliferative response among tendon fibroblasts and mesenchymal stem cells is diminished within the shoulder. This inadequate healing response therefore transfers the burden of tendon reattachment and integrity to the mechanical strength of the sutures. Over time, the sutures break down and tear away from bone and/or tendon, causing re-injury of the shoulder. The problem has been documented in numerous studies employing the use of animal models. Coleman and colleagues report in The Journal of Bone and Joint Surgery 85:2391-2402 (2003) that the repaired infraspinatus muscle of the shoulder is capable of producing only 63% of the normal contraction force normal at 12 weeks after repair using a sheep model of chronic injury.
In view of the problems associated with rotator cuff repairs, it would be desirable to provide compositions and methods operable to improve the healing response associated with rotator cuff repairs. In particular, it would be desirable to provide compositions and methods which enhance fibrotic and proliferative responses among tendon fibroblasts and mesenchymal stems cells thereby promoting healing of a torn rotator cuff and tendon reattachment to the humeral head.